List of List into List

[mp3909]

How do you make this list ['Tokyo','London',['Paris','Madrid']] into this list ['Tokyo','London','Paris','Madrid']?

[nilamo]

Taking a nested data structure, with multiple levels, and turning it into a single level, is known as "flattening".  There's many ways to do it, recursion is (I think) the way that's normally suggested, that way it can handle a list within a sublist within the list.

Maybe like this?

>>> cities = ["Tokyo", "London", ["Paris", "Madrid"]]
>>> def flatten(items):
...   for item in items:
...     if isinstance(item, list):
...       yield from flatten(item)
...     else:
...       yield item
...
>>> list(flatten(cities))
['Tokyo', 'London', 'Paris', 'Madrid']

[buran]

It would be nice if you provide more information on how do you get this structure, i.e. it may be a problem with how you create it in the first place.

[mp3909]

I was just practicing some stuff on list comprehensions and wanted to see how you go about using list comprehensions to create a single list from a list of list where at least one of the elements in the list is not necessarily an element within a sub-list

For example, it was easy for me to create a single list using list comprehension from the following list [['Tokyo','London'],['Madrid','Paris']], you could simply do:

>>>oList= [['Tokyo','London'],['Madrid','Paris']]
>>>newList = [item for sublist in oList for item in sublist]
>>>newList
['Tokyo', 'London', 'Madrid', 'Paris']

but how would you go about using list comprehensions to create a single list when you have a list like this ['Tokyo','London',['Madrid','Paris']] - makes the problem a little more difficult because using the above approach yields the following result (which is wrong):

>>> oList = ['Tokyo','London',['Madrid','Paris']]
>>> newList = [item for sublist in oList for item in sublist]
>>> newList
['T', 'o', 'k', 'y', 'o', 'L', 'o', 'n', 'd', 'o', 'n', 'Madrid', 'Paris']

I hope that clarifies my problem and would appreciate it if anyone out there knows how to solve this using list comprehensions.
Thank You.

[nilamo]

The first step, is getting all the items to be the same:

>>> oList = ['Tokyo','London',['Madrid','Paris']]
>>> [item if isinstance(item, list) else [item] for item in oList]
[['Tokyo'], ['London'], ['Madrid', 'Paris']]

From there, you can use what you already have:

>>> oList = ['Tokyo','London',['Madrid','Paris']]
>>> [subitem for item in [x if isinstance(x, list) else [x] for x in oList] for subitem in item]
['Tokyo', 'London', 'Madrid', 'Paris']

[Windspar]

more examples

newList = [item for items in oList for item in [[items], items][isinstance(items, list)]]

newList = [item for items in oList for item in (items if isinstance(items, list) else [items])]

is_list = lambda l: l if isinstance(l, list) else [l]
newList = [item for items in oList for item in is_list(items)]